GaN Self-Standing Substrate Thermal Conductivity and Mobility Optimization
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Solution Overview
Problem
Nitride-based semiconductor devices face challenges in achieving high thermal conductivity and electron mobility while maintaining sufficient electrical conductivity, as high carrier concentrations typically reduce thermal conductivity and increase dislocation density, leading to inefficient heat dissipation and light extraction.
Innovation Solution
A GaN self-standing substrate with a diameter of 25 mm or more and a thickness of 250 micrometers, featuring a n-type carrier concentration of 1.2×10^18 cm^-3 to 3×10^19 cm^-3, thermal conductivity of 1.2 W/cmK to 3.5 W/cmK, and electron mobility within specific ranges, achieved through methods such as extended HCl gas contact with the Ga melt, use of nanomasks with microscopic pores, and early transition to facet-growth planes to reduce impurity concentrations and enhance crystalline quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the carrier concentration is increased to secure sufficient electrical conductivity, then the electrical conductivity is improved, but the thermal conductivity is reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the carrier concentration within the range of 1.2×10^18 cm^-3 to 3×10^19 cm^-3. This optimized parameter range allows the GaN substrate to achieve sufficient electrical conductivity for device operation while maintaining thermal conductivity above 1.2 W/cmK, thus resolving the contradiction between electrical and thermal conductivity requirements
Solution Approach 2:
The patent implements local quality by creating a layered structure where the GaN substrate has optimized doping for electrical conductivity, while the epitaxial layers grown on top have different compositional and doping characteristics tailored for their specific functions. This allows different regions to have different properties optimized for their local requirements
2Reliability
If the carrier concentration is increased to secure sufficient electrical conductivity, then the electrical conductivity is improved, but the dislocation density is increased
Solution Approach 1:
The patent applies preliminary action by first growing a high-quality GaN substrate with controlled carrier concentration and low dislocation density before epitaxial growth. The substrate is prepared in advance with optimized crystalline structure, and then epitaxial layers are grown on this pre-prepared foundation, preventing dislocation propagation from the substrate to the device layers
Solution Approach 2:
The patent segments the device structure into a separately optimized GaN substrate and epitaxial device layers. The substrate is fabricated with specific doping levels for electrical conductivity, while the epitaxial layers are grown with controlled composition and doping to achieve device functionality with minimal dislocation density
3Temperature
If a SiC substrate is used to enhance heat dissipation, then the thermal conductivity is improved, but the light extraction efficiency is reduced
Solution Approach 1:
The patent uses a GaN substrate as an intermediary material between the heat dissipation requirement and light extraction requirement. The GaN substrate has intermediate thermal conductivity (1.2-3.5 W/cmK) that provides adequate heat dissipation, while its optical properties allow high light extraction efficiency, thus mediating between the conflicting requirements of SiC (high thermal conductivity but low light extraction) and sapphire (low thermal conductivity but high light extraction)
Solution Approach 2:
The patent changes the material parameter from SiC or sapphire to GaN for the substrate, which fundamentally alters both thermal and optical properties. This material substitution enables simultaneous achievement of adequate thermal conductivity for heat dissipation and high optical transparency for light extraction, resolving the contradiction between heat dissipation and light extraction efficiency
Data Source
AI summary
A nitride-based semiconductor substrate has a diameter of 25 mm or more, a thickness of 250 micrometers or more, a n-type carrier concentration of 1.2×1018 cm−3 or more and 3×1019 cm−3 or less, and a thermal conductivity of 1.2 W/cmK or more and 3.5 W/cmK or less. Alternatively, the substrate has an electron mobility μ [cm2/Vs] of more than a value represented by logeμ=17.7−0.288 logen and less than a value represented by logeμ=18.5−0.288 logen, where the substrate has a n-type carrier concentration n [cm−3] that is 1.2×1018 cm−3 or more and 3×1019 cm−3 or less.